The vertical cavity surface emitting laser (VCSEL) has several advantages over its edge-emitting cousin. Its strengths include a higher modulation speed, on-wafer testing and the emission of a symmetrical emission pattern that is oriented perpendicular to the surface. This form of emission is ideal for coupling into other optical components.
This emission pattern is also well suited for configuring multiple devices into a two-dimensional array. However, all these merits over edge-emitting lasers come at the expense of a more complex device architecture.
With a VCSEL, resonator mirrors have to fulfil two roles: like an edge-emitter, they have to control the extent of optical feedback and light output; but in addition, they also have to be electrically conducting, so that they can allow the injection of carriers from the contacts into the active region.